Conventionally, a vehicle-mounted antenna device includes an antenna base, a cover covering the antenna base, and an antenna element and a circuit board accommodated in a space enclosed by the antenna base and the cover. In order to prevent the antenna element and the circuit board from being wet by moisture entering from outside, there is a technology of providing a sealing member enclosing the entirety of an outer perimeter of the antenna base (e.g., Japanese Laid-Open Patent Publication No. 2013-229813). The sealing member disclosed in Japanese Laid-Open Patent Publication No. 2013-229813 is secured, with an adhesive, a two-sided tape or the like, to a groove provided around a recessed portion that is located at a center of the antenna base and accommodates the circuit board.